Failures of electric motors


Electric motors failures

Mechanical and electrical problems can lead to engine failures. It is therefore important to know the possible causes in order to consider preventive maintenance actions before the machines are unavailable and create financial losses as well as production impossibilities which can lead to customer dissatisfaction.

Winding insulation breaks and bearing wear are the two main causes of engine failure, but these problems themselves result from very different reasons. 

The causes of failures

Group 1: quality of the power supply
- Transient voltage.
- Voltage imbalance.
- Harmonic distortion.

Group 2: Frequency converters
- Drive output PWM signals.
- Stray current.
- Motor overloads.

Group 3: Mechanical part of the engine
- Incorrect alignment of the output shaft.
- Tree imbalance.
- Loosening of the shaft.
- Wear of bearings.

Group 4: Mechanical part linked to an installation
- Unstable or wobbly foot support.
- Pipe constraint.
- Shaft tension

Transient voltage

Transient voltages can be from different sources, internal or external to the site. High power activated or deactivated loads, the commissioning of reactive energy compensation capacitor banks, meteorological disturbances due to lightning, possible operations of the energy distributor, can generate transient voltages.
These transient voltages, which vary in amplitude and frequency, risk degrading the insulation of the motor windings.
Identifying the source of these transient voltages can be difficult as their appearances can be random, and their symptoms can present in different ways.
For example, a transient voltage can appear on control cables which are not directly responsible for the damage, but can nevertheless disrupt the operation of the systems.
Impact: Degradation of the insulation of the motor windings may short-circuit them.

It is therefore important to monitor the supply voltages, and to choose drives with input supply surge suppression components to protect the drive from the risk of transient voltages.
It may also be necessary to install surge arresters at the head of the electrical installation.

Voltage imbalance

Three-phase distribution systems often supply single-phase loads.
Any imbalance in impedance or load distribution may cause an imbalance on all three phases.
Potential failures can come from the motor wiring, its terminations, or even the windings themselves.
This imbalance can cause stress on all phase circuits of a three-phase system.
At the simplest level, all three voltage phases should always have the same magnitude.
Impact: the imbalance generates excessive current flow on one or more phases, which increases operating temperatures and degrades insulation.
Separate the three-phase and single-phase load power supplies.


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